1. Field of the Invention
The present invention relates to a color cathode-ray tube, and more particularly to, a color cathode-ray tube easily detaching a shadow mask by expanding a gap (Q-value) between the shadow mask and a phosphor screen by a positive number times when manufacturing the phosphor screen with the same resolution degree as existing color cathode-ray tubes.
2. Description of the Related Art
In general, a color cathode-ray tube is a display device in which an electron gun emits an electron beam toward a phosphor screen applied with a plurality of green (G), blue (B), and red (R) phosphor layers for emitting light, such that a predetermined picture is obtained, and mainly used in a monitor of a household television set and a computer due to the low price and the good screen quality thereof.
Herein, a shadow mask having a plurality of beam passage apertures is arranged in front of the phosphor screen facing the electron gun, and three electron beams emitted from the electron gun are joined at an beam passage aperture, separated when passing the beam passage aperture and thereafter land on the corresponding red (R), green (G) and blue (B) phosphor layers within the phosphor screen, so that the exact color is obtained.
For example, a path of an electron beam of a cathode-ray tube can be looked at. An in-line type electron gun emits three electron beams red, green and blue in parallel on a horizontal axis. A phosphor screen receiving the electron beams repeatedly forms a plurality of red, green and blue phosphor stripes. A shadow mask arranged between the electron gun and the phosphor screen forms a beam passage aperture corresponding to one group of red, green and blue phosphor layers.
Three electron beams emitted from the electron gun are focused in one beam passage aperture, and intersected with side red electron beam and blue electron beam centering on the central green electron beam while passing the beam passage aperture for landing on the corresponding blue, green and red phosphor layers of the phosphor screen. In such a case, the gap between the shadow mask and the phosphor screen is maintained at the existing Q-value, the adjacent blue, green and red phosphor layers emit light by three electron beams red, green, and blue passed through one beam passage aperture.
In the above structure of the cathode-ray tube, the gap between the shadow mask and the phosphor screen, that is, the Q-value is designed by the geometric combination of the electron gun and the phosphor screen.
Important measurements concerning the color cathode-ray tube are the distance from the electron gun to the phosphor screen, especially a distance from a green electron beam passage hole formed in a final electrode of the electron gun to a central point of the phosphor screen, a horizontal pitch of the shadow mask, that is, a distance between centers of the beam passage apertures adjacent to each other in a horizontal direction, and a screen pitch of the phosphor screen, that is, a distance between centers of green phosphor layers adjacent to each other in a horizontal direction. Also important is the gap between the central green electron beam and side red or blue electron beam in a main focus lens, which is called the S value of the electron gun.
The Q-value of the cathode-ray tube is determined according to the S value of the electron gun, the horizontal pitch of the shadow mask and the distance from the electron gun to the phosphor screen. A spherical difference of an electric lens may be reduced and focus characteristic may be improved as the value S of the electron gun becomes larger. However, as the S value of the electron gun becomes larger, a diameter of a neck part becomes expanded, such that there are disadvantages that the power consumption required for deflection of the electron beam increases and convergence characteristics are degraded.
The distance from the electron gun to the phosphor screen is proportional to a screen size and inversely proportional to a deflection angle of the electron beam, which is appropriately determined by considering the screen size and a deflection angle of the electron beam before designing the Q-value.
In the state that the S value and the distance from the electron gun to the phosphor screen are appropriately determined, the Q-value is proportional to the horizontal pitch of the shadow mask. However, since the horizontal pitch of the shadow mask as well as the screen pitch of the phosphor screen should be designed at a small value for obtaining a high resolution cathode-ray tube, the Q-value of the cathode-ray tube becomes smaller in proportion to the horizontal pitch of the shadow mask to achieve a high resolution.
However, during the manufacturing process of the phosphor screen, a process for detaching a mask assembly formed with a shadow mask and a mask frame to a panel, is generated over 4 times basically for exposing operation. At this time, if a screen pitch is about 0.4 mm (millimeters) in a conventional shadow mask, the Q-value is about 5xcx9c6 mm. Such a very small Q-value causes a problem in detaching the mask assembly.
That is, in such case that the Q-value is very small, there is difficulty in exactly remounting the mask assembly as the originally designed value Q over the whole screen during a process for remounting the mask assembly and there are problems of causing inferiority of the phosphor screen if the Q-value deviates even in one part of the screen, and lowering the quality of the screen by disturbing the exact landing of the electron beams when operating the cathode-ray tube.
The inventor of the present invention has filed the invention titled Shadow Mask Type Colour Cathode-Ray Tube for preventing a moire phenomenon of a cathode-raytube (Korean Patent Publication No. 94-5493). Herein, the inventor set the Q-value so that the side red and blue electron beams passed through a beam passage aperture reintersect with other blue and red electron beams before landing on the phosphor layer, and the Q-value is twice as large as the Q-value set in the existing cathode-ray tube.
Therefore, the above invention has an advantage that a user can not recognize the moire phenomenon on the screen and the assembling operation for a mask assembly can be easily performed by expanding the Q-value. However, there is a limit in improving the assembling efficiency of the mask assembly.
Exemplars of the art are U.S. Pat. No. 6,013,400 issued to LaPeruta et al. for Method Of Manufacturing A Luminescent Screen Assembly For A Cathode-Ray Tube, U.S. Pat. No. 5,610,473 issued to Yokota et al. for Color Cathode-Ray Tube, U.S. Pat. No. 5,929,559 issued to Sano et al. for Cathode Ray Tube, U.S. Pat. No. 5,506,467 issued to Nishimura et al. for Cathode-Ray Tube And Method Of Manufacturing The Same, U.S. Pat. No. 5,365,143 issued to Nishimura et al. for Color Cathode Ray Tube Having A Plurality Of Masks, U.S. Pat. No. 5,634,837 issued to Nishimura et al. for Cathode-Ray Tube And Method Of Manufacturing The Same, U.S. Pat. No. 5,506,466 issued to Shoda et al. for Color Cathode-Ray Tube, U.S. Pat. No. 5,691,597 issued to Nishimura et al. for Color Cathode-Ray Tube And Method For Manufacturing The Same, U.S. Pat. No. 4,708,680 issued to Kanto et al for Color Picture Tube And Method For Manufacturing The Same, U.S. Pat. No. 5,803,781 issued to Nishimura et al. for Method Of Assembling Shadow Mask Of CRT Panel, U.S. Pat. No. 5,760,539 issued to Park for CRT Having A Panel With A Smaller Effective Area And Straight Outlines, U.S. Pat. No. 4,136,300 issued to Morrell for Cathode Ray Tube Having Improved Shadow Mask, U.S. Pat. No. 6,139,387 issued to Kimura et al. for Method For Manufacturing A Color Cathode Ray Tube, U.S. Pat. No. 5,604,395 to Nishirnura et al. discloses Color Cathode-Ray Tube Having Substantially Flat Face And Rear Plates Opposing Each Other, and U.S. Pat. No. 5,365,142 to Nishimura et al. for Cathode-Ray Tube Wherein Plural Regions Of Phosphor Screen Are Scanned Independently Of One Another. 
It is therefore an object of the present invention to provide a color cathode-ray tube, in which the gap between the shadow mask and a phosphor screen (Q-value) is expanded by a positive number times to improve the manufacturing yield and the quality of the cathode-ray tube by easily detaching a mask assembly when manufacturing a phosphor screen, thereby obtaining the same resolution degree as existing color cathode-ray tubes.
It is another object is to have a cathode-ray tube that can be easily manufactured and yet not reduce the picture quality of the cathode-ray tube.
It is yet another object to have a method of increasing the quality of the color cathode-ray tubes through expanding the distance between the shadow mask and a phosphor screen.
It is still yet another object to have a color cathode-ray tube that can increase the efficiency of mask assembly and yet maintain the resolution of the cathode-ray tube.
In order to achieve the above and further objects of the present invention, a color cathode-ray tube includes a phosphor screen formed on the inner surface of a panel and repeatedly forming a plurality of red, green and blue phosphor stripes, an electron gun for emitting three electron beams toward the phosphor screen, and a shadow mask arranged in front of the phosphor screen facing the electron gun and forming a plurality of beam passage apertures for separating the electron beams, where the shadow mask is mounted on an inside of the panel to satisfy values Q and Qxe2x80x2 of the following formula, and the side red and blue electron beams of the three electron beams joined at one beam passage aperture after being emitted, arrive at the corresponding red and blue phosphor layers beyond (nxe2x88x921) phosphor layers centering on the green phosphor where the central green electron beam arrived,
Qxe2x80x2=nQ (nxe2x89xa74) 
where Qxe2x80x2 denotes a gap between the shadow mask and the phosphor screen, n denotes a natural number except multiples of 3 and is larger than or equal to 4, and Q denotes a gap between a shadow mask and a phosphor screen when three electron beams joined at one beam passage aperture land in one group of red, greeb and blue phosphor layers arranged on the phosphor screen side by side.
As above, since the convergence characteristic of the electron beam of arriving the phosphor screen has not changed even in case that the Q-value is expanded by a positive number of times, the present invention has an advantage of easily detaching a mask assembly when manufacturing the phosphor screen by the expanded Q-value with the same resolution degree as the existing cathode-ray tube.